1. Field of the Invention
The invention relates generally to locking pliers, and more particularly, to locking pliers having an improved locking and release mechanism.
2. Description of Related Art
Pliers having locking mechanisms to maintain the pliers jaws in a fixed position are well known. Such pliers typically include an adjustment mechanism that sets the pliers jaws at roughly a desired distance apart, and a toggle mechanism locks the pliers about a workpiece when the pliers handles are squeezed together. In known locking pliers, the action of squeezing the handles together drives the toggle mechanism beyond a "dead center point," to lock the jaws onto the workpiece.
Known locking pliers typically include a fixed handle and jaw with a movable jaw coupled thereto. The movable jaw is operated by a movable lever that has one end coupled to the movable jaw. The opposite end of the movable lever defines a movable handle. A link member connects the fixed handle to a forward section of the movable lever intermediate the movable handle and the movable jaw. The combination of the link member and the forward section of the movable lever constitute the toggle mechanism for locking and releasing the pliers. An adjustment mechanism, such as an adjustment screw, laterally moves the end of the link member connected to the fixed handle to adjust the separation of the fixed and movable jaws. A spring may be employed, for example, between the movable jaw and the fixed handle, to normally bias the jaws apart.
The above described arrangement of the link member and forward section of the movable lever define three pivot points around which the locking mechanism of typical prior art locking pliers operates. The first pivot point is the point at which the movable lever connects to the movable jaw. The second pivot point is located where the link member connects to the forward section of the movable lever, and the third pivot point occurs at the opposite end of the lever member, where the link member connects to the fixed handle.
When the locking pliers handles are apart (jaws apart, or open), the toggle mechanism (the forward section of the movable lever and the link member) forms an obtuse angle. As the handles are brought together, the jaws close towards each other, and the angle formed by the toggle mechanism approaches a straight line. The "dead center point" occurs when toggle member forms a straight line; in other words, when the three pivot points are in a line. As the handles continue to move together, the second pivot point passes the dead center point, and movement of the movable handle is halted, usually by the one or both of the forward section of the movable lever or the link member contacting a stop or the fixed handle. The jaws will maintain their closed position until the second pivot point is forced back across the dead center point by actuation of a release lever or other actuator provided on the fixed handle.
Unfortunately, there are several shortcomings associated with known locking pliers, such as those described above using a "dead center point" locking operation. First, the action of releasing the locked pliers jaws by pushing the middle pivot point back across the dead center point often requires two hands. The user has one hand gripping the handles of the pliers, and the user's other hand is required to activate the release. This two-hand requirement is simply unacceptable for many tasks requiring the use of a pair of pliers.
Further, the jaws of prior art locking pliers will lock any time the handles are manipulated such that the middle pivot point crosses the dead center point. Often, it is desirable to operate a locking pliers as a spring loaded pliers, for example, to achieve a "ratcheting" action when turning a nut or bolt. However, with known locking pliers, the jaws lock each time the handles are squeezed together, and the release mechanism must be actuated to unlock the pliers. This necessitates repeatedly locking and unlocking the pliers whenever repeated opening and closing of the jaws is required.
Moreover, the release lever of many prior art locking pliers may cause an uncontrolled or unintentional unlocking of the pliers. The release mechanisms of typical prior art locking pliers perform the unlocking function by pushing the center pivot point back across the dead center point. Once the center pivot point passes the dead center point from the locked position, the jaws are not maintained in their closed position. Further, since most known locking pliers are spring biased to an open position (jaws apart), as soon as the center pivot point passes the dead center point, the pliers will "spring" open. This can create several difficulties.
For example, if the locking pliers are being used in a clamping operation, the pliers will completely release if the release lever is inadvertently activated. During operations requiring locking and unlocking of the pliers, the user often does not have a free hand available to activate the release lever. Hence, the user may be required to release his grip from the handles, at least partially, to activate the release. If the user does not maintain control of the handles when the release is activated, the pliers may spring out of the user's hands, or possibly spring open and strike the user's hand.
Still further, many prior art locking pliers designs have a toggle mechanism including the link member described above, extending between the fixed handle and the movable lever. The combination of the handles and the link member produce various "pinch points." These pinch points are locations where material, such as a user's clothes or a finger, may be caught and pinched as the handles are moved relative to each other.
Thus, a need exists for locking pliers that address these, and other, shortcomings of the prior art.